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9.4. Modifying Text

We can loop through the string and modify it using find and slice (substring).

Google has been digitizing books. But, sometimes the digitizer makes a mistake and uses 1 for i. The following program replaces 1 with i everywhere in the string. Now you might not want to really replace every 1 with i, but don’t worry about that right now. It uses a while loop since we don’t know how many times it will need to loop.

Activity: CodeLens 9.4.1 (Change_Ones)

You don’t have to replace just one character. You could replace every instance of a word with another word. For example, what if you spelled a word wrong and wanted to change it everywhere?

Activity: CodeLens 9.4.2 (Change_Word)

Can you loop through and encode a string to hide the contents of the message?

Activity: CodeLens 9.4.3 (Encode_String)

What character is e replaced with when the message is encoded?

• a
• The letter in str is replaced with the letter at the same position in eStr.
• d
• The letter in str is replaced with the letter at the same position in eStr.
• w
• Try counting the letters in str to figure out how many letters to count in eStr.
• v
• The letter e is at position 4 in str and will be replaced with the letter v at position 4 in eStr.

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What is the value of encodedMessage after the loop executes the first time?

• ""
• It starts out as the empty string, but a letter is added each time through the loop.
• "o"
• The letter in str is replaced with the letter at the same position in eStr.
• "n"
• The letter in eStr at the same position as the m in str is n.
• "m"
• Notice that we are adding the letter in eStr at pos not the letter in str at pos.

The program below decodes an encoded message, but the lines are mixed up. Put the lines in the right order with the right indentation.

        message = ""
str = "abcdefghijklmnopqrstuvwxyz. "
eStr = "zyxwvutsrqponmlkjihgfedcba ."
encodedMessage = "nvvg.nv.zg.nrwmrtsg"
---
for letter in encodedMessage:
---
    pos = eStr.find(letter)
---
    message = message + str[pos:pos+1]
---
print(message)
        

Write the code to replace every 0 with o in the given string ‘The 0wl h00ts l0udly’.

str = "The 0wl h00ts l0udly" # SET POS TO A VALUE GREATER THAN OR EQUAL TO 0 pos = 1 # SET WHILE CONDITION while pos >= 0: # REPLACE VALUE pos = str.find("0") if pos == -1: break str = str[0:pos] + "o" + str[pos+1:len(str)] # PRINT RESULT print(str)

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